|M.Sc Student||Andrey Torotko|
|Subject||Preparation of New Group 4 Amidinate and Triazenide|
Complexes and their Activity in the Polymerization
|Department||Department of Chemistry||Supervisor||Full Professor Eisen Moris|
|Full Thesis text|
During the research over bis(benzamidinate) group 4 complexes, it was found that in the polypropylene polymerization in presence of methylaluminoxane (MAO), one of the benzamidinate ligands migrates to the Al center, while the other benzamidinate ligand undergoes rearrangement and coordinates to metal center, probably decreasing the monomer insertion rate. In order to neutralize this effect we changed the aromatic ring substituent to hydrogen. An additional parameter we wanted to study was the central ligand atom effect; as such, we changed an inner carbon atom in the amidinate ligand to nitrogen, producing a triazenide ligand. Another family of promising bis-chelated non metallocene catalyst is the bis(phenoxy-imine) group 4 transition metal complexes, known as phenoxyimine (FI) catalysts. One of the most important things discovered for some of the phenoxyimine (FI) catalysts, is the controlled (co)polymerization of olefinic monomers and the living polymerization process. The important factor to create a living polymerization was proposed to be at least one ortho-fluorine at the aryl group (based on density functional theory (DFT) calculations) producing a week attractive and electrostatic interaction between the ortho-F and a β-H at the growing chain. By this interaction, it's possible to avert unwanted β-H transfer reactions. In order to check this assumption in our complexes, we substituted the aryl group in the bis(formamidinate) group 4 metal complexes with an ortho-fluorinated ligand. In this paper we report the synthesis and characterization of group 4 amidinate and triazenide complexes, describe the catalytic activity of the complexes towards the polymerization of ethylene and propylene in presence of methylaluminoxane (MAO) and trityl tetrakis(pentafluorophenyl)borate (TTPB) as co-catalysts, and with triisobutylaluminium (TIBA) as alkylating agent and activator, producing high density polyethylene and atactic/isotactic polyethylene. The molecular structures of complexes 2, 6 and 7 have been confirmed by X-ray studies. The molecular structure of these complexes has been confirmed by nuclear magnetic resonance (NMR) 1H, 13C, and 19F, 1H-1H correlation spectroscopy (COSY) and elemental analysis. In these complexes the metal is octahedral, bound to the two κ2 chelating ligands and two cis-dimethylamido groups, exhibiting a C2-like symmetry. Complexes 3, 6, 7 and 8 showed a dynamic behavior in solution as a dependence on temperature. This dynamic behavior was studied and supposed to be due to a disconnection and recoordination of the chelating ligands through the metal-nitrogen bond, resulting in the formation of different octahedral stereoisomers in solution.